Frequency Distribution System Research Articles

Radio Frequency System, Power Converters and Cryomodule installation and tests as a Polish in-kind contribution to the European Spallation Source (ESS)

The European Spallation Source (ESS) project currently enters the final stage of installation. Since 2017, a group of engineers and technicians from The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Science (IFJ PAN) are involved in the project. The contribution to the project can be divided into three main tasks: Radio Frequency Distribution System (RFDS), RF (Radio Frequency) Power Stations and Cryomodules.The RFDS in ESS project is one of the largest installations of this type consisting of 155 RF high power systems. Engineers and technicians from IFJ PAN were responsible for preparation, installation and RF measurements of the above-mentioned system. The team is also involved in preparation and conducting low and high power tests of the RF stations.The IFJ PAN team is also responsible for the preparation as well as vacuum and cryogenic tests for 9 Medium and 21 High Beta Cryomodules, before they are installed in the tunnel.The advanced quality control and quality assurance were mandatory for this work because the costs of failures, as well as potential delays, would have a huge impact in the project realisation. Therefore dedicated methods and approaches have been adapted to this work using experience gained by the IFJ PAN team on previous projects like LHC, XFEL and W7X.

Stable frequency transfer for clock synchronization for telecom networks

A stable and reliable clock synchronization system that transfers reference clocks to nodes is essential for telecom networks. Mainly, the clock synchronization of telecom networks is carried out through satellite links. However, for the evolving ubiquitous wireless communications, especially in some harsh environments, such as underground and trenches, the satellite-based clock synchronization scheme bears inevitable obstacles, which may cause strategic risks for the telecom networks, since no control and manipulation can be imposed on the satellite systems. Therefore, to ensure the robust operation of telecom networks with performance guarantees, some auxiliary means are desirable to assist clock synchronization that is solely based on satellite links. In this article, we report a phase-stabilized frequency signal transmission on branching optical fiber for clock synchronization for telecom networks. Particularly, the phase fluctuation due to optical carriers separation link and fiber link is compensated by a feedback network, which employs a high-precision voltage-controlled oscillator in the phase-locked loop to drive the acousto-optic frequency shifter for fast phase correction. Furtherly, the factors that cause performance limitations of the frequency distribution system are analyzed. Eventually, the experiment results obtained show that a stabilized fiber-optic frequency transfer scheme can be used as a reliable method for clock synchronization with high accuracy.

Design of Building Heating System Based on Distributed Variable Frequency Pump

With the continuous development and progress of society, people’s requirements for living conditions have gradually changed. They begin to pursue the comfort and personalization of the living environment, while also pay more and more attention to the problems of energy and environment. In order to build a suitable living environment, the implementation of central heating is bound to consume all kinds of resources. In the heating process, the efficient use and effective saving of energy has become an important measure for the heating industry to achieve the coordinated development of energy and environment. Taking the central heating as the research object and the secondary side distributed variable frequency pump heating transmission and distribution system as the goal, this paper studies the energy saving of the distributed variable frequency pump heating transmission and distribution system. This paper provides a design method of distributed variable frequency pump heating transmission and distribution system, in order to provide some basis for the design of distributed variable frequency pump heating transmission and distribution system in the future, and solve the problem of high energy consumption in the traditional central heating transmission and distribution system.

A Low Computational Complexity Algorithm of PTS Technique for PAPR Reduction in the 4G and 5G Systems

The (OFDM) defined as orthogonal multiplex frequency distribution system is very popular of the design of waveforms for high speed data communication in 4G wireless technology. In addition, a filter-based waveform design, such as filtered OFDM (F-OFDM), has been proposed as a candidate for the 5G technology waveform in order to overcome the current weaknesses of OFDM. And 5G requirements. The high average peak ratio (PAPR) is taken as the main obstacle to OFDM and remains an inherent problem with F-OFDM since both systems support orthogonal transmission. In this study, a new efficient algorithm called groupings of complex variants of PTS (G-C-PTS) was proposed to reduce the level of high complexity in PTS. G-C-PTS can significantly reduce complexity with a slight decrease in PAPR performance compared to traditional PTS. In addition, comparisons were made between (OFDM) and (F-OFDM) systems based on the GC-PTS algorithm for PAPR, bit error rate (BER) and spectral power density (PSD) to validate the proposed algorithm. Partial transmit sequence (PTS) procedure is considered one of the production strategies to decrease the high peak-to-average power ratio (PAPR) in the 4G waveform plane, for example multiplex frames for symmetric repetition division (OFDM).

VCSEL polarization modulation for pulse-per-second clock signal transfer in optical frequency distribution systems

In this paper, a novel vertical cavity surface emitting laser (VCSEL) polarization modulation technique based on polarization switching due to thermal heating in a single transverse mode class 10 G VCSEL at 1 310 nm is demonstrated experimentally. The inherent orthogonal polarization switching of the VCSEL carrier with changing bias is exploited in the transmission of pulse-per-second (PPS) timing clock signal. Experimental results show that PPS pulse widths of 9.97 μs and 9.98 μs are measured for back-to-back analysis and over 3.21 km of G 652 urban fibre transmission, respectively. This work provides a novel alternative for adoption in optical frequency and time transfer applications.

A simple-architecture fibered transmission system for dissemination of high stability 100 MHz signals.

We report on the development of a simple-architecture fiber-based frequency distribution system used to transfer high frequency stability 100 MHz signals. This work is focused on the emitter and the receiver performances that allow the transmission of the radio-frequency signal over an optical fiber. The system exhibits a residual fractional frequency stability of 1 × 10-14 at 1 s integration time and in the low 10-16 range after 100 s. These performances are suitable to transfer the signal of frequency references such as those of a state-of-the-art hydrogen maser without any phase noise compensation scheme. As an application, we demonstrate the dissemination of such a signal through a 100 m long optical fiber without any degradation. The proposed setup could be easily extended for operating frequencies in the 10 MHz-1 GHz range.

Frequency Reference Stability and Coherence Loss in Radio Astronomy Interferometers Application to the SKA

The requirements on the stability of the frequency reference in the square Kilometer array (SKA), as a radio astronomy interferometer, are given in terms of the maximum accepted degree of coherence loss caused by the instability of the frequency reference. In this paper, we analyze the relationship between the characterization of the instability of the frequency reference in the radio astronomy array and the coherence loss. The calculation of the coherence loss from the instability characterization given by the Allan deviation is reviewed. A model of a typical frequency distribution system is presented. The verification of the coherence and frequency reference stability requirements is discussed. Some practical aspects and limitations relevant to the SKA are analyzed.

Co-location of space geodetic techniques carried out at the Geodetic Observatory Wettzell using a closure in time and a multi-technique reference target

The quality of the links between the different space geodetic techniques (VLBI, SLR, GNSS and DORIS) is still one of the major limiting factors for the realization of a unique global terrestrial reference frame that is accurate enough to allow the monitoring of the Earth system, i.e., of processes like sea level change, postglacial rebound and silent earthquakes. According to the specifications of the global geodetic observing system of the International Association of Geodesy, such a reference frame should be accurate to 1 mm over decades, with rates of change stable at the level of 0.1 mm/year. The deficiencies arise from inaccurate or incomplete local ties at many fundamental sites as well as from systematic instrumental biases in the individual space geodetic techniques. Frequently repeated surveys, the continuous monitoring of antenna heights and the geometrical mount stability (Losler et al. in J Geod 90:467–486, 2016. https://doi.org/10.1007/s00190-016-0887-8 ) have not provided evidence for insufficient antenna stability. Therefore, we have investigated variations in the respective system delays caused by electronic circuits, which is not adequately captured by the calibration process, either because of subtle differences in the circuitry between geodetic measurement and calibration, high temporal variability or because of lacking resolving bandwidth. The measured system delay variations in the electric chain of both VLBI- and SLR systems reach the order of 100 ps, which is equivalent to 3 cm of path length. Most of this variability is usually removed by the calibrations but by far not all. This paper focuses on the development of new technologies and procedures for co-located geodetic instrumentation in order to identify and remove systematic measurement biases within and between the individual measurement techniques. A closed-loop optical time and frequency distribution system and a common inter-technique reference target provide the possibility to remove variable system delays. The main motivation for the newly established central reference target, locked to the station clock, is the combination of all space geodetic instruments at a single reference point at the observatory. On top of that it provides the unique capability to perform a closure measurement based on the observation of time.

ELSTAB-Fiber-Optic Time and Frequency Distribution Technology: A General Characterization and Fundamental Limits.

In this paper, we present an overview of the electronically stabilized (thus named ELSTAB) fiber-optic time and frequency (T&F) distribution system based on our idea of using variable electronic delay lines as compensating elements. Various extensions of the basic system, allowing building a long-haul, multiuser network are described. The fundamental limitations of the method arising from fiber chromatic dispersion and system dynamics are discussed. We briefly characterize the main hardware challenge of the system, which is the design of a pair of low-noise, precisely matched delay lines. Finally, we present experimental results with T&F distribution over up to 615km of fiber, where we demonstrate frequency stability in the range of 1-7 ×10(-17) for 10(5) s averaging and time calibration with accuracy well below 50ps. Also, practical implementation of the ELSTAB in the Polish T&F distribution network is shown.

Mechanisms and Industry Solutions for RF Interference in a Co-located Network

Radio frequency interference (RFI) in a co-located network is a major challenge faced by cellular network operators. The RFI issues are prominent when the radio frequency transceivers consisting of two or more co-located networks operate within close or adjacent frequency bands. This paper presents the mechanisms of RFI caused by spurious emission and receiver blocking in a co- located network and proffer industry solution through the application of various mitigation techniques. One method may reduce a particular type of interference to a certain level, a combination of two or more methods can conveniently reduce the interference to an acceptable level. The advent of smart-phones and affordable mobile communication services has led to an exponential growth in the wireless subscriber's base. This rapid increase motivated the mobile network operators to build more cell sites to enhance better coverage and improved quality service delivery. The drive to meet this goal by the network operators has led to incessant proliferation of new cell towers which are capital intensive. In this regard, a co-location, which has recently become a common network build-out strategy, where different cellular systems share a common site, space and structures for the location of base station active equipment and the Radio Frequency (RF) distribution system. It was introduced by the International

Implementation and characterization of a stable optical frequency distribution system

An optical frequency distribution system has been developed that continuously delivers a stable optical frequency of 268 THz (corresponding to a wavelength of 1118 nm) to different experiments in our institute. For that purpose, a continuous wave (cw) fiber laser has been stabilized onto a frequency comb and distributed across the building by the use of a fiber network. While the light propagates through the fiber, acoustic and thermal effects counteract against the stability and accuracy of the system. However, by employing proper stabilization methods a stability of 2 x 10(-13) tau(-1/2) is achieved, limited by the available radio frequency (RF) reference. Furthermore, the issue of counter-dependant results of the Allan deviation was examined during the data evaluation.

Analysis of the transition from the Einstein crystal model to the Debye model

We discuss the low-temperature specific heat of a system consisting of a small number of particles constituting a simple lattice and analyse its dependence on the number of particles, on their frequency distribution and on the dimensionality of the crystal. The results are compared with those expected either in a non-interacting particle model (Einstein crystal) or in a continuous frequency distribution system (Debye model); they show that a number of particles of the order of a few tens is sufficient to give a good agreement with the Debye model. The analysis of the effects of the frequency split indicates that the Debye model is satisfied when the frequency separation is of the order of 80% of the fundamental frequency. The dependence of the results on the sample dimensionality is discussed. The results are valid for other thermodynamic functions such as the energy or the entropy.

Development of an ultrastable fiber optic frequency distribution system using an optical delay control module [for frequency standard and VLBI

An ultrastable fiber optic frequency distribution system is described. The ultrastable phase stability is achieved by configuring a closed phase-locked loop with a single-mode optical fiber transmission line in which two optical carrier signals with different wavelengths are transmitted as a forward and a backward signal, and installing an optical delay control module which has no differential dispersion effect between the two optical carrier waves and induces no electrical noise. A phase stabilized optical fiber (PSOF) is used for the signal transmission line. The stabilities of this system are 7.5/spl times/10/sup -17/ and 1.1/spl times/10/sup -17/ in Allan standard deviation at 1000 and 10000 s averaging time, respectively, while the environmental temperature of the PSOF cable varies as much as the range of 10/spl deg/C and the rate of 10/spl deg/C/12 h.

Hybrid high frequency AC power distribution architecture for telecommunication systems

A novel high frequency hybrid power distribution system for telecommunication applications is presented. The proposed hybrid system combines the advantages of both the sinusoidal voltage and current types of high frequency distribution systems and it has advantages such as connectorless power transfer, fuseless protection, sinusoidal voltage and current distribution and, high overall system efficiency. The different operating modes of the proposed power distribution system are described in detail and performance characteristics are presented. Finally experimental results are given to validate the concepts developed and to demonstrate the system performance.

Phase stabilization of widely separated oscillators

Techniques for reducing propagation-induced phase fluctuations in frequency distribution systems are discussed and compared. Examples of both microwave and optical methods are presented. Stabilization to a few parts in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10^{8}</tex> over a 15-km path seems to be feasible.

Remote control carrier systems in two-way closed-circuit educational TV

“Person to person” type of instruction is made possible by the use of a radio rather thafi a video frequency distribution system. This also permits use of modulated carrier controls which greatly increases the flexibility of the presentation.